Metastasis is main reason for cancer death and has been shown to be controlled by specific genetic events. The complex nature of metastasis from the primary site to a distant site involves acquisition of many phenotypes which makes the genetics of the process very complex. Individual processes such as cell movement, migration and invasion are central to the process and understanding the multitude of controlling mechanisms in this process is vital to understand metastasis and designing therapies against the process. We have shown that expression of the WAVES gene is a critical facilitator of in vitro and in vivo cell invasion and metastasis in breast cancer cells. In human primary breast cancer, significant up regulation of the WAVES protein is seen in advanced stage tumors compared with low grade tumors. In a mouse model of metastasis using MDA-MB-231 cells, siRNA knockdown of WAVES significantly reduces metastasis potential. Immunocytochemistry shows that loss of WAVES function affects the normal organization of actin structures that are related to cell movement and that this effect is mediated through an interaction with PIS Kinase. Knockdown of WAVES results in a failure of lamellipodia formation which is responsible for the restricted cell movement observed. In model cell systems, WAVES appears to control the invasion phenotype through the regulation of MMP production through the p38 pathway. Our preliminary data demonstrating the mechanism of how WAVES controls cellular invasion and migration has provided important clues to another key regulator of these phenotypes which impact on metastasis in vivo. To understand the function of WAVES more fully it will be important therefore to determine the regulator controls of this gene and the pathways it is involved in, since this will likely provide new insights into the regulation of cellular invasion. In this application we propose a series of proteomics approaches to identify the proteins that interact with WAVES to obtain a better understanding of the pathways it is involved in. We also propose a series of experiments using siRNA and somatic cell knockout to eliminate WAVES function in specific cells to evaluate the importance of specific protein-protein interactions. Finally we have designed a series of experiments to probe more deeply into the mechanisms of WAVES function. Since expression of WAVES promotes invasion, it is an attractive potential target for therapy against metastasis, which after all is the lethal phase of cancer progression in most cases. A better understanding of the intracellular regulatory pathways governing the function of WAVES, therefore, may provide new opportunities for therapeutic intervention.